I propose to examine the genetic and enzymic relationships between the mechanisms which cut and fragment DNA and those which participate in recombination. The systems studied are the restriction and modification of newly formed or transferred DNA of phage lambda and the interaction of these processes with those of recombination and repair. Mutants differing in recombination and repair proficiency will be studied in vivo and in vitro for the contribution that their residual recombination systems make to degradation and recombination of restricted DNA. The objective of this work is the evaluation of the relative roles of the restriction and recombination systems in processing DNA.